Pensana’s plan to become one of the world’s major suppliers of magnet metal rare earths took a major step forward this week with receipt of approvals for funding the $268 million first phase of its flagship Longonjo project, in Angola.
Tapping the likes of the Africa Finance Corporation, Absa Bank Limited and the Angolan Sovereign Wealth Fund, the company says it now has the cash in its coffers to get to its phase 1 design capacity of 20,000 t/y of mixed rare earth carbonate (MREC).
Having hit this milestone, IM investigated the design of this operation to see how the company plans to extract, concentrate, calcine and chemically refine the near surface material to make that MREC product.
The project currently under development comprises an open pit, concentrator and recovery plants, tailings storage facility (TSF, designed to meet the requirements of the Global Industry Standard on Tailings Management (GISTM)), process water supply, bulk power supply, mine infrastructure, workshops, offices, accommodation village, recreational facilities and other associated infrastructure.
Site infrastructure works commenced in 2023 with construction activities commencing last year as part of an early works program.
The open-pit operation is predominantly free-dig, with a Pensana spokesperson saying minimal work is required ahead of mining the initial pits, other than clearing and grubbing the topsoil (300-500 mm), which will be stockpiled for concurrent rehabilitation purposes as the pits progress. The primary in-pit and blending stockpile management equipment includes two 74-t hydraulic shovels, five 35-t payload ADTs, two grade control drill rigs and six wheel loaders.
The spokesperson added: “Ancillary equipment dedicated to haul road and stockpile maintenance includes track and wheel dozers, graders, fuel and water trucks, vibrating compact rollers, telehandlers and light duty vehicles. The majority of this equipment will be supplied as part of the mining and stockpile management contract.”
Grupo Nov, an Angola-based civil and earthworks contractor, has been established on site for the past year during the early works program. It has been preparing the construction camp, process plant and contractors’ laydown area, as well as clearing and compacting, upgrading roads and managing stormwater to ensure minimal disruption during the rainy season, Pensana says. Its existing fleet on site will be expanded as main construction activities increase.
“Based on extensive large and small diameter drill core data to date, no blasting is anticipated until late in the life of the mine when mining approaches the weathered/hard-rock interface, ranging between 30-70 m,” the spokesperson said. “Occasionally less weathered boulders will be set aside as they are encountered (if any) during the initial five-to-seven years.”
From the run-of-mine pad, the ore goes through a scrubbing/milling circuit before reagents are added ahead of two-stage flotation. Pensana, last year, placed an order with NCP International, a global supplier of new and refurbished comminution equipment based in South Africa, for the $2.3 million ball mill for the concentrator plant. The concentrate is then thickened ahead of the refinery, while the remainder goes to final tailings thickening before placement in the TSF.
The TSF is one of the elements reinforcing Pensana’s “Responsible Mining” approach at Longonjo, with the company stating on its website that construction and operation will be allied with ESG best practice including alignment to the GISTM.
The spokesperson explained: “The development of the tailings solution has gone through many iterations to arrive at the current solution, taking a conservative approach to the TSF design. This includes thickened tailings spigotted deposition into a double-HDPE-lined, penstock TSF, fully recycled to process water for zero discharge and reduced water consumption.”
Thickened tailings via mechanical compaction, plus accelerated mud compaction on the TSF, are being considered and has worked well on similar tailings characteristics and rheology, according to the spokesperson. “This has the potential to significantly reduce the ultimate life of mine TSF footprint and is intended to be introduced following trials in the commissioning phase but is currently excluded from the design,” the spokesperson added.
When it comes to the refinery, concentrate drying and filtration is the first step ahead of acid mixing and baking. CCD leaching follows, with nano filtration and impurity removal stages coming ahead of the MREC precipitation. The CCD leaching and impurity removal steps also generate a tailings stream that is neutralised ahead of moving onto final thickening and TSF placement. A MREC product is produced that Pensana intends to ship via Lobito Port, some 270 km away by rail.
Based on a reserve of 30 Mt at 2.55% total rare earth oxides (for 166,000 t of NdPrO reserves), Longonjo has a mine life of over 20 years. Therefore, a phase two expansion is also in the pipeline to double output to 40,000 t/y of MREC.
If it gets to this scale, the mine will, by current estimates, produce around 5% of the world’s production in the form of a high value MREC, capable of being converted into permanent magnets for electric vehicles and offshore wind turbines, the company says.
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